@MaxFromUA At this point there's a little bug on android reason why you can't choose a team there.
GB is already working on it to fix that a.s.a.p. In the mean time please use the website to choose your team.

@MaxFromUA Ah now it's clear. slots are unlocked by experience last slot is 50 experience there for you can't choose a team through website.
So I'm sorry but there's no bug there, since the other slots should not have unlocked either.
For now you can only choose teams through app.